High speed image sensors have been widely used in many applications in different fields including the automotive field, the machine vision field, and the field of professional video photography. The technology used to manufacture image sensors, and in particular, complementary-metal-oxide-semiconductor (CMOS) image sensors, has continued to advance at great pace. For example, the demand of higher frame rates and lower power consumption has encouraged the further miniaturization and integration of these image sensors.
In addition to the frame rate and power consumption demands, image sensors are also subjected to performance demands. The quality and accuracy of the pixel readouts cannot be compromised to accommodate the increase in frame rate or power consumption.
One way to increase the frame rate of a CMOS image sensor may be to increase the number of readout circuits operating in parallel. However, in current image sensors, the minimum time interval in between two successive image captures is about 4 milliseconds (ms). Given that the short exposure is much less than 4 milliseconds (e.g., 1 ms), the timing gap between this short exposure and the subsequent image capture is 3 milliseconds. Similarly, the ultra-short exposure is about 0.25 ms such that the timing gap between this ultra-short exposure and the subsequent image capture is 3.75 milliseconds. The ratio between successive exposure times is 4:1. Accordingly, the current image sensors readout quality suffers due to this large timing gap between successive image captures which degrades image quality (e.g., ghost issues).
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.